This invention relates to coolant pumps and more particularly, to a multistage sealed direct drive centrifugal pump which is especially useful in X-ray tube cooling systems.
For the cooling of an X-ray tube such as used in a CT system, a coolant liquid is circulated around the X-ray tube to cool the tube during use. A pump is employed to circulate the coolant in a cooling system and X-ray system specifications require that the pump have stringent characteristics to be properly employed in the X-ray system. More particularly, the pump must be hermetically sealed, have no shaft seals, add minimal heat to the cooling system, run clean and contaminant free over an extended period of time, produce minimal electrical noise, and be of minimal weight and physical size. In addition, the pump is exposed to high G forces due to rotation of the CT machine and it would therefore be desirable to have a pump of small size and weight.
A known pump for cooling X-ray tubes employs a single impeller to propel the coolant around the X-ray tube. Gear pumps are also known for X-ray tube cooling. A single stage pump has a relatively large diameter impeller to generate the requisite pressure, and the disk friction of the impeller is relatively high by reason of the large diameter. As a consequence, known single impeller pumps have lower efficiency. In addition, the large diameter impeller increases the thrust of the impeller on the motor shaft on which it is mounted and therefore the motor bearings must be sufficient to handle the increased thrust or motor life can be reduced because of the relatively higher thrust. The cooling requirements have increased with increasing X-ray tube power and performance and thereby require increased coolant pumping flow rates and pressure to achieve intended cooling performance. It is therefore desirable to provide a pump providing higher flow rate and pressure than present pumps while providing the necessary characteristics required for use in an X-ray cooling system.